ak4647 AKM Semiconductor, Inc., ak4647 Datasheet - Page 34

• Manufacturer Part Number: ak4647
• Description: Stereo Codec With Mic/hp-amp
• Manufacturer: AKM Semiconductor, Inc.

ASAHI KASEI
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM1-0 bits (Table 26) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 23) during the wait time, the ALC
recovery operation is done. The IVL and IVR values are automatically incremented by RGAIN1-0 bits (Table 27) up to
the set reference level (Table 28) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 25).
Then the IVL and IVR are set to the same value for both channels. The ALC recovery operation is done at a period set by
WTM1-0 bits. When zero cross is detected at both channels during the wait period set by WTM1-0 bits, the ALC recovery
operation waits until WTM1-0 period and the next recovery operation is done.
For example, when the current IVOL value is 30H and RGAIN1-0 bits are set to “01”, IVOL is changed to 32H by the
auto limiter operation and then the input signal level is gained by 0.75dB (=0.375dB x 2). When the IVOL value exceeds
the reference level (REF7-0), the IVOL values are not increased.
When
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
the waiting timer of ALC recovery operation starts.
The ALC operation corresponds to the impulse noise. When the impulse noise is input, the ALC recovery operation
becomes faster than a normal recovery operation. When large noise is input to microphone instantaneously, the quality of
small level in the large noise can be improved by this fast recovery operation.
MS0566-E-00
“ALC recovery waiting counter reset level (LMTH1-0) ≤ Output Signal < ALC limiter detection level (LMTH1-0)”
“ALC recovery waiting counter reset level (LMTH1-0) > Output Signal”,
WTM1
0
0
1
1
WTM0
RGAIN1
0
1
0
1
REF7-0
0
0
1
1
EFH
F1H
F0H
E2H
E1H
E0H
03H
02H
01H
00H
Table 28. Reference Level at ALC Recovery operation
Table 26. ALC Recovery Operation Waiting Period
:
:
1024/fs
128/fs
256/fs
512/fs
Table 27. ALC Recovery GAIN Step
RGAIN0
0
1
0
1
GAIN(dB)
+35.625
+30.375
+29.625
−53.625
+35.25
−53.25
MUTE
ALC Recovery Operation Waiting Period
+36.0
+30.0
−54.0
128ms
8kHz
16ms
32ms
64ms
:
:
- 34 -
1 step
2 step
3 step
4 step
GAIN STEP
16kHz
16ms
32ms
64ms
8ms
0.375dB
0.375dB
0.750dB
1.125dB
1.500dB
Step
Default
44.1kHz
11.6ms
23.2ms
Default
2.9ms
5.8ms
Default
[AK4647]
2006/11